The invention relates to a method of measuring the eccentricity of a waveguide embedded in a cylindrical connector pin.
In waveguide connector pairs the end faces of waveguides to be coupled must be fixedly and centrically embedded in cylindrical connector pins. The optical axes of the coupled waveguides should preferably be in exact alignment (compare DE-AS 2,159,327 which corresponds substantially to U.S. Pat. No. 3,800,388 issued Apr. 2, 1974). Since the outer surface of the connector serves as a reference surface for aligning the connector pair, the eccentricity of, for example, a monomode waveguide should be less than 0.5 .mu.m if sufficiently small connector attenuations are to be achieved. An accuracy of at least 100 nm should be observed in inspection measurements. Relative to the diameter of the connector sleeve of approximately 1.25 mm, this is a relative accuracy of 8.times.10.sup.-5.
Known measuring method for measuring the eccentricity of the core of a waveguide relative to its outer cladding surface (for example as described in "Image Sharing Technique", "Fiber Optic Bulletin No. 10 of the Vickers Instruments, 1984") are not suitable for this purpose.
One object of the invention is to provide a measuring method of the type described in the opening paragraph i.e. a method for measuring the eccentricity of a waveguide embedded in a cylindrical connector pin, and to provide a suitable measuring device.
This object is achieved in a method wherein the optical center of the end face of the waveguide is introduced into the mechanical axis of rotation of a distance sensor scanning the outer surface of the connector pin and subsequently the eccentricity of the waveguide is determined form the measuring values obtained during the relative rotation of the distance sensors along the outer surface of the connector pin.
A condition for achieving the desired accuracy is that the relative rotation of the distance sensor about the circumference of the connector pin is effected by means of high-precision bearings. Commercially available shape measuring machines suitable for the purpose described in the present invention have rotational spindles whose eccentricity is less than 40 nm.
Mechanical feelers as well as optically operating devices of known types of suitable as distance sensors. Suitable devices of sufficient measuring accuracy in the nm range are commercially available.
According to the invention a multitude of values measured along the circumference of the connector pin is taken into account for determining the eccentricity of the waveguide so that irregularities of the connector surface do not invalidate the measuring value.
The optical center--generally the center of the end face of a waveguide core--should be introduced into the mechanical axis of rotation with great accuracy, namely with an offset of possibly less than 10 nm. This is preferably accomplished by means of optical adjusting methods in which the light passage between the waveguide arranged in the connector pin and a sensor waveguide arranged substantially coaxially thereto--or reversely--serves as a criterion for achieving the target position. Such adjusting methods are generally known for adjusting two waveguides to be connected.
Very sensitive methods of this type as described in DE-PS 2626243 are particularly suitable.
In a preferred embodiment of the method according to the invention, opposite the end face of the connector pin, a light source or light receiver is arranged which rotates eccentrically around the mechanical axis of rotation, and the connector pin is moved into such a position that a minimum is reached for the fluctuating part of the light energy, which light energy is coupled by the light transmitter into the waveguide or by the waveguide into the light receiver, and which light energy fluctuates in dependence upon the angle of rotation.
However, in an especially preferred embodiment, opposite the end face of the waveguide arranged in the connector pin, a light transmitter or a light receiver is arranged fixedly and eccentrically relative to the mechanical axis of rotation and the connector pin, which is arranged on a mount rotatable about the mechanical axis of rotation, is aligned in such a way that a minimum is reached for the fluctuating part of the light energy coupled by the light transmitter into the waveguide or by the waveguide into the light receiver. This light energy fluctuates in dependence upon the angle of rotation when rotating said pin.
Preferably, the radiation from the light transmitter or to the light receiver is directed via a sensor waveguide to the waveguide arranged in the connector pin. The direction of receiving or transmitting light can then be fixed in a uniform manner, resulting in a narrow light beam.
A possible angle offset of the optical axis of the waveguide relative to the center line of the connector pin can be measured in hat the beam axis of the sensor waveguide is inclined relative to the mechanical axis of rotation and in that the direction of the axis of the connector pin is positioned in such an angle relative to the mechanical axis of rotation that a minimum value is reached for the part of the coupled-in light energy which is dependent on the angle of rotation.
Since in general both the eccentricity and also the angle offset of the waveguide must be measured, it is preferred to move the connector pin axially parallel to the mechanical axis of rotation until a minimum is reached for the part of the coupled in light energy which is dependent on the angle of rotation and to subsequently move the angle position of the connector pin relative to the mechanical axis of rotation while maintaining the position of its end face, preferably, this is accomplished in such a way that substantially the value "zero" is reached for the part of the coupled-in light energy which is dependent on the angle of rotation.
Preferred arrangements for performing the method according to the invention comprise a mount that is rotatable about a mechanical axis of rotation and devices by which a distance sensor scanning the outer surface of the connector pin is rotatable about the mechanical axis of rotation relative to the connector pin. In such arrangements, preferably the connector pin is clamped in a mount arranged on a rotary table which is rotatable about the mechanical axis of rotation and is axially parallel movable relative thereto. Preferably, a sensor waveguide is fixedly connected to the bearing housing of the rotatory table in such a way that its optical axis is eccentric relative to the mechanical axis of rotation of the rotary table and the distance sensor is secured to the bearing housing. In this preferred arrangement also preferably the axis of the sensor waveguide is inclined relative to the mechanical axis of rotation and means are provided for changing the angle of the axial direction of the connector pin.
An alternative method which is particularly suitable for test measurements is characterized in that the connector pin is rotated around its geometrical central axis; a sensor waveguide is arranged substantially axially parallel opposite the end face of the waveguide to be measured, such that its optical axis is offset relative to the mechanical axis of rotation of the connector pin; and the fluctuation amplitude of the light energy coupled by the waveguide to be measured into the sensor waveguide, or conversely, is measured.